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Fikret Kargi - One of the best experts on this subject based on the ideXlab platform.

  • Dark fermentation of ground wheat starch for bio-hydrogen production by fed-Batch Operation
    International Journal of Hydrogen Energy, 2009
    Co-Authors: Fikret Kargi, M. Yunus Pamukoglu
    Abstract:

    Abstract Ground wheat solution was used for bio-hydrogen production by dark fermentation using heat-treated anaerobic sludge in a completely mixed fermenter operating in fed-Batch mode. The feed wheat powder (WP) solution was fed to the anaerobic fermenter with a constant flow rate of 8.33 mL h−1 (200 mL d−1). Cumulative hydrogen production, starch utilization and hydrogen yields were determined at three different WP loading rates corresponding to the feed WP concentrations of 10, 20 and 30 g L−1. The residual starch (substrate) concentration in the fermenter decreased with Operation time while starch consumption was increasing. The highest cumulative hydrogen production (3600 mL), hydrogen yield (465 mL H2 g−1 starch or 3.1 mol H2 mol−1 glucose) and hydrogen production rate (864 mL H2 d−1) were obtained after 4 days of fed-Batch Operation with the 20 g L−1 feed WP concentration corresponding to a WP loading rate of 4 g WP d−1. Low feed WP concentrations (10 g L−1) resulted in low hydrogen yields and rates due to substrate limitations. High feed WP concentrations (30 g L−1) resulted in the formation of volatile fatty acids (VFAs) in high concentrations causing inhibition on the rate and yield of hydrogen production.

  • ethanol fermentation of cheese whey powder solution by repeated fed Batch Operation
    Enzyme and Microbial Technology, 2007
    Co-Authors: Serpil Ozmihci, Fikret Kargi
    Abstract:

    Abstract Ethanol fermentation of cheese whey powder (CWP) solution was realized in a fed-Batch operated fermenter using the pure culture of Kluyveromyces marxianus (DSMZ 7239) at different feed CWP concentrations varying between 51 and 408 g l −1 . Total sugar content of the feed varied between 25 and 200 g l −1 with a constant flow rate of 0.084 l h −1 . Sugar utilization, ethanol formation and biomass growth were investigated as function of the feed sugar concentration in a five-cycle repeated fed-Batch Operation where the system reached the quasi steady-state. Variations of the growth and the product yield coefficients with the feed sugar concentration were quantified. The growth yield coefficient ( Y X / S ) decreased with increasing feed sugar concentrations. The product yield coefficient ( Y P / S ) was almost constant (0.54 ± 0.02 g EtOH g −1 S ) for sugar concentrations between 25 and 150 g l −1 , but decreased at the feed sugar concentration of 200 g l −1 due to high osmotic pressure at high sugar concentrations. The highest ethanol concentration (63 g l −1 ) and the productivity (5.3 g EtOH h −1 ) were obtained with a 125 g l −1 feed sugar concentration and sugar loading rate of 10.5 g  S  h −1 .

  • Adsorbent supplemented biological treatment of pre-treated landfill leachate by fed-Batch Operation.
    Bioresource Technology, 2004
    Co-Authors: Fikret Kargi, M. Yunus Pamukoglu
    Abstract:

    Abstract Biological treatment of landfill leachate usually results in low COD removals because of high chemical oxygen demand (COD), high ammonium-N content and presence of toxic compounds. Coagulation–flocculation with lime addition and air stripping of ammonia were used as pre-treatment in this study in order to improve biological treatability of the leachate. Pre-treated leachate was subjected to adsorbent supplemented biological treatment in an aeration tank operated in fed-Batch mode. COD and NH 4 -N removal performances of powdered activated carbon (PAC) and powdered zeolite (PZ) were compared during biological treatment. Adsorbent concentrations varied between 0 and 5 g l −1 . Percent COD and ammonium-N removals increased with increasing adsorbent concentrations. Percent COD removals with PAC addition were significantly higher than those obtained with the zeolite. However, zeolite performed better than the PAC in ammonium-N removal from the leachate. Nearly 87% and 77% COD removals were achieved with PAC and zeolite concentrations of 2 g l −1 , respectively. Ammonium-N removals were 30% and 40% with PAC and zeolite concentrations of 5 g l −1 , respectively at the end of 30 h of fed-Batch Operation.

  • Aerobic biological treatment of pre-treated landfill leachate by fed-Batch Operation
    Enzyme and Microbial Technology, 2003
    Co-Authors: Fikret Kargi, M. Yunus Pamukoglu
    Abstract:

    Abstract Landfill leachate obtained from the solid waste landfill area contained high chemical oxygen demand (COD) and ammonium ions which resulted in low COD and ammonium removals by direct biological treatment. COD and ammonium ion contents of the leachate were reduced to reasonable levels by chemical precipitation with lime and air stripping of ammonia. The pre-treated leachate was subjected to aerobic biological treatment in an aeration tank by fed-Batch Operation. The effects of the feed wastewater COD content and flow rate on COD and ammonium ions removal were investigated. Nearly 76% COD and 23% NH 4 -N removals were obtained after 30 h of Operation with a flow rate of 0.21 l h −1 and the feed COD content of 7000 mg COD l −1 . COD removal efficiency decreased with increasing COD loading rates. A kinetic model for COD removal was developed and the kinetic constants were determined by using the experimental data.

  • Simultaneous adsorption and biological treatment of pre-treated landfill leachate by fed-Batch Operation
    Process Biochemistry, 2003
    Co-Authors: Fikret Kargi, M. Yunus Pamukoglu
    Abstract:

    Abstract Due to high chemical oxygen demand (COD), ammonium–N content and presence of toxic compounds such as heavy metals, direct biological treatment of landfill leachate results in low removal efficiencies. In order to improve biological treatability of the leachate, coagulation–flocculation and air stripping of ammonia were used as pre-treatment. Pre-treated leachate was treated biologically using an aeration tank operated in fed-Batch mode in the absence and presence of powdered activated carbon (PAC) as adsorbent. PAC addition improved COD removal significantly especially at concentrations above 0.5 g l −1 . However, improvements in COD removals were marginal for PAC concentrations above 2 g l −1 . Nearly 86% COD removal was achieved with 2 g l −1 PAC added biological treatment whereas, COD removals by only biological oxidation and only PAC adsorption were nearly 74 and 38%, respectively at the end of 30 h of fed-Batch Operation. An empirical equation was developed to describe the contribution of adsorption over biological treatment as a function of PAC concentration.

M. Yunus Pamukoglu - One of the best experts on this subject based on the ideXlab platform.

  • Dark fermentation of ground wheat starch for bio-hydrogen production by fed-Batch Operation
    International Journal of Hydrogen Energy, 2009
    Co-Authors: Fikret Kargi, M. Yunus Pamukoglu
    Abstract:

    Abstract Ground wheat solution was used for bio-hydrogen production by dark fermentation using heat-treated anaerobic sludge in a completely mixed fermenter operating in fed-Batch mode. The feed wheat powder (WP) solution was fed to the anaerobic fermenter with a constant flow rate of 8.33 mL h−1 (200 mL d−1). Cumulative hydrogen production, starch utilization and hydrogen yields were determined at three different WP loading rates corresponding to the feed WP concentrations of 10, 20 and 30 g L−1. The residual starch (substrate) concentration in the fermenter decreased with Operation time while starch consumption was increasing. The highest cumulative hydrogen production (3600 mL), hydrogen yield (465 mL H2 g−1 starch or 3.1 mol H2 mol−1 glucose) and hydrogen production rate (864 mL H2 d−1) were obtained after 4 days of fed-Batch Operation with the 20 g L−1 feed WP concentration corresponding to a WP loading rate of 4 g WP d−1. Low feed WP concentrations (10 g L−1) resulted in low hydrogen yields and rates due to substrate limitations. High feed WP concentrations (30 g L−1) resulted in the formation of volatile fatty acids (VFAs) in high concentrations causing inhibition on the rate and yield of hydrogen production.

  • Adsorbent supplemented biological treatment of pre-treated landfill leachate by fed-Batch Operation.
    Bioresource Technology, 2004
    Co-Authors: Fikret Kargi, M. Yunus Pamukoglu
    Abstract:

    Abstract Biological treatment of landfill leachate usually results in low COD removals because of high chemical oxygen demand (COD), high ammonium-N content and presence of toxic compounds. Coagulation–flocculation with lime addition and air stripping of ammonia were used as pre-treatment in this study in order to improve biological treatability of the leachate. Pre-treated leachate was subjected to adsorbent supplemented biological treatment in an aeration tank operated in fed-Batch mode. COD and NH 4 -N removal performances of powdered activated carbon (PAC) and powdered zeolite (PZ) were compared during biological treatment. Adsorbent concentrations varied between 0 and 5 g l −1 . Percent COD and ammonium-N removals increased with increasing adsorbent concentrations. Percent COD removals with PAC addition were significantly higher than those obtained with the zeolite. However, zeolite performed better than the PAC in ammonium-N removal from the leachate. Nearly 87% and 77% COD removals were achieved with PAC and zeolite concentrations of 2 g l −1 , respectively. Ammonium-N removals were 30% and 40% with PAC and zeolite concentrations of 5 g l −1 , respectively at the end of 30 h of fed-Batch Operation.

  • Aerobic biological treatment of pre-treated landfill leachate by fed-Batch Operation
    Enzyme and Microbial Technology, 2003
    Co-Authors: Fikret Kargi, M. Yunus Pamukoglu
    Abstract:

    Abstract Landfill leachate obtained from the solid waste landfill area contained high chemical oxygen demand (COD) and ammonium ions which resulted in low COD and ammonium removals by direct biological treatment. COD and ammonium ion contents of the leachate were reduced to reasonable levels by chemical precipitation with lime and air stripping of ammonia. The pre-treated leachate was subjected to aerobic biological treatment in an aeration tank by fed-Batch Operation. The effects of the feed wastewater COD content and flow rate on COD and ammonium ions removal were investigated. Nearly 76% COD and 23% NH 4 -N removals were obtained after 30 h of Operation with a flow rate of 0.21 l h −1 and the feed COD content of 7000 mg COD l −1 . COD removal efficiency decreased with increasing COD loading rates. A kinetic model for COD removal was developed and the kinetic constants were determined by using the experimental data.

  • Simultaneous adsorption and biological treatment of pre-treated landfill leachate by fed-Batch Operation
    Process Biochemistry, 2003
    Co-Authors: Fikret Kargi, M. Yunus Pamukoglu
    Abstract:

    Abstract Due to high chemical oxygen demand (COD), ammonium–N content and presence of toxic compounds such as heavy metals, direct biological treatment of landfill leachate results in low removal efficiencies. In order to improve biological treatability of the leachate, coagulation–flocculation and air stripping of ammonia were used as pre-treatment. Pre-treated leachate was treated biologically using an aeration tank operated in fed-Batch mode in the absence and presence of powdered activated carbon (PAC) as adsorbent. PAC addition improved COD removal significantly especially at concentrations above 0.5 g l −1 . However, improvements in COD removals were marginal for PAC concentrations above 2 g l −1 . Nearly 86% COD removal was achieved with 2 g l −1 PAC added biological treatment whereas, COD removals by only biological oxidation and only PAC adsorption were nearly 74 and 38%, respectively at the end of 30 h of fed-Batch Operation. An empirical equation was developed to describe the contribution of adsorption over biological treatment as a function of PAC concentration.

Jo Shu Chang - One of the best experts on this subject based on the ideXlab platform.

  • Exploring the potency of integrating semi-Batch Operation into lipid yield performance of Chlamydomonas sp. Tai-03.
    Bioresource technology, 2019
    Co-Authors: Chung Hong Tan, Pau Loke Show, Tau Chuan Ling, Dillirani Nagarajan, Duu-jong Lee, Wei Hsin Chen, Jo Shu Chang
    Abstract:

    Third generation biofuels, also known as microalgal biofuels, are promising alternatives to fossil fuels. One attractive option is microalgal biodiesel as a replacement for diesel fuel. Chlamydomonas sp. Tai-03 was previously optimized for maximal lipid production for biodiesel generation, achieving biomass growth and productivity of 3.48 ± 0.04 g/L and 0.43 ± 0.01 g/L/d, with lipid content and productivity of 28.6 ± 1.41% and 124.1 ± 7.57 mg/L/d. In this study, further optimization using 5% CO2 concentration and semi-Batch Operation with 25% medium replacement ratio, enhanced the biomass growth and productivity to 4.15 ± 0.12 g/L and 1.23 ± 0.02 g/L/d, with lipid content and productivity of 19.4 ± 2.0% and 239.6 ± 24.8 mg/L/d. The major fatty acid methyl esters (FAMEs) were palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2). These short-chain FAMEs combined with high growth make Chlamydomonas sp. Tai-03 a suitable candidate for biodiesel synthesis.

  • The effects of feeding criteria on the growth of oleaginous yeast—Rhodotorula glutinis in a pilot-scale airlift bioreactor
    Journal of The Taiwan Institute of Chemical Engineers, 2015
    Co-Authors: Jo Shu Chang
    Abstract:

    Abstract Rhodotorula glutinis is an oleaginous microorganism, which is being able to accumulate great amounts of total lipid. To achieve high cell density cultivation, the fed-Batch Operation was adopted. The effects of three feeding strategies on the growth of R. glutinis in a pilot scale of 50 L airlift bioreactor were examined. Results indicate that Operation in a 50 L airlift bioreactor had superior performance on the growth of R. glutinis than that of the 15 L agitation tank. The fed-Batch Operation could provide sufficient carbon source—crude glycerol while avoiding inhibition resulting from the accumulation of high crude glycerol. Therefore, fed-Batch Operation appears to promote a higher cell density as compared to that of Batch Operation. Among the feeding criteria, the exponential feeding criteria could ease the observed growth-lag phase by avoiding peaks in crude glycerol concentration. As such, it led to the highest obtained cell growth rate. Nevertheless, the conventional pulse feeding criteria could achieve the highest total lipid and β-carotene productivity. Consequently, if collecting the maximum total lipids for biodiesel production is the goal, the fed-Batch Operation by pulse feeding is suggested as a suitable criterion for the cultivation of R. glutinis with crude glycerol as the carbon source.

  • the effects of feeding criteria on the growth of oleaginous yeast rhodotorula glutinis in a pilot scale airlift bioreactor
    Journal of The Taiwan Institute of Chemical Engineers, 2015
    Co-Authors: Jo Shu Chang
    Abstract:

    Abstract Rhodotorula glutinis is an oleaginous microorganism, which is being able to accumulate great amounts of total lipid. To achieve high cell density cultivation, the fed-Batch Operation was adopted. The effects of three feeding strategies on the growth of R. glutinis in a pilot scale of 50 L airlift bioreactor were examined. Results indicate that Operation in a 50 L airlift bioreactor had superior performance on the growth of R. glutinis than that of the 15 L agitation tank. The fed-Batch Operation could provide sufficient carbon source—crude glycerol while avoiding inhibition resulting from the accumulation of high crude glycerol. Therefore, fed-Batch Operation appears to promote a higher cell density as compared to that of Batch Operation. Among the feeding criteria, the exponential feeding criteria could ease the observed growth-lag phase by avoiding peaks in crude glycerol concentration. As such, it led to the highest obtained cell growth rate. Nevertheless, the conventional pulse feeding criteria could achieve the highest total lipid and β-carotene productivity. Consequently, if collecting the maximum total lipids for biodiesel production is the goal, the fed-Batch Operation by pulse feeding is suggested as a suitable criterion for the cultivation of R. glutinis with crude glycerol as the carbon source.

  • Effects of pH and fermentation strategies on 2,3-butanediol production with an isolated Klebsiella sp. Zmd30 strain
    Bioresource Technology, 2013
    Co-Authors: Chiao Ling Wong, Jo Shu Chang
    Abstract:

    Abstract This study examined the effects of pH-controlled and fermentation strategies on 2,3-butanediol (2,3-BDO) production by an isolated Klebsiella sp. Zmd30 strain. The pH value of 6.0 was found to be optimal among the investigated range of 4.5–9.0. In Batch fermentation, the concentration, productivity and yield of 2,3-BDO were 57.17 g/l, 1.59 g/l/h and 82%, respectively. The 2,3-BDO production by Klebsiella sp. Zmd30 was found to be growth-associated. Higher 2,3-BDO concentration (110 g/l) and yield (94%) was obtained by using fed-Batch Operation, but the productivity was lower (0.88 g/l/h) as compared to that when using Batch Operation. The highest 2,3-BDO productivity of 2.81 g/l/h was obtained with the continuous culture at a hydraulic retention time (HRT) of 12 h. The results suggest that fed-Batch Operation might be most suitable for commercialized 2,3-BDO production, due to obtaining a high concentration and yield.

Tai Hyun Park - One of the best experts on this subject based on the ideXlab platform.

  • Hydrogen production from formic acid in pH-stat fed-Batch Operation for direct supply to fuel cell.
    Bioresource technology, 2009
    Co-Authors: Jong-hwan Shin, Jong Hyun Yoon, Tai Hyun Park
    Abstract:

    Enterobacter asburiae SNU-1 harvested after cultivation was used as a whole cell biocatalyst, for the production of hydrogen. Formic acid was efficiently converted to hydrogen using the harvested cells with an initial hydrogen production rate and total hydrogen production of 491 ml/l/h and 6668 ml/l, respectively, when 1 g/l of whole cell enzyme was used. Moreover, new pH-stat fed-Batch Operation was conducted, and total hydrogen production was 1.4 times higher than that of Batch Operation. For practical application, bio-hydrogen produced from formic acid using harvested cells was directly applied to PEMFC for power generation.

  • Hydrogen production from formic acid in pH-stat fed-Batch Operation for direct supply to fuel cell.
    Bioresource technology, 2009
    Co-Authors: Jong-hwan Shin, Jong Hyun Yoon, Tai Hyun Park
    Abstract:

    Enterobacter asburiae SNU-1 harvested after cultivation was used as a whole cell biocatalyst, for the production of hydrogen. Formic acid was efficiently converted to hydrogen using the harvested cells with an initial hydrogen production rate and total hydrogen production of 491 ml/l/h and 6668 ml/l, respectively, when 1 g/l of whole cell enzyme was used. Moreover, new pH-stat fed-Batch Operation was conducted, and total hydrogen production was 1.4 times higher than that of Batch Operation. For practical application, bio-hydrogen produced from formic acid using harvested cells was directly applied to PEMFC for power generation.

  • fed Batch Operation of recombinant escherichia coli containing trp promoter with controlled specific growth rate
    Biotechnology and Bioengineering, 1994
    Co-Authors: Sung Kwan Yoon, Whan Koo Kang, Tai Hyun Park
    Abstract:

    A feb-Batch Operation for the production of bovine somatotropin (bST) under the control of tryptophan promoter in Escherichia coli was investigated. The plasmid used contains a two-cistron system and altered codon usage for higher expression of bST. Specific growth rate is an important parameter in the fermentation, because it affects the production of growth-inhibitory organic acids and the expression of recombinant protein. The feeding rate was adjusted to keep the specific growth rate constant in this study. The variable growth yield expressed as a function of time was used for the calculation of the feeding rate. The growth yield decreases during the fermentation as product expression is induced. The specific growth rate was well controlled; however, intracellular bST concentration decreased at high cell concentrations. This is considered to be due to degradation by proteases. The decrease was prevented by an exponential feeding of the yeast extract as an organic nitrogen source. © 1994 John Wiley & Sons, Inc.

Andrés Illanes - One of the best experts on this subject based on the ideXlab platform.

  • Comparison of Batch and repeated Batch Operation of lactulose synthesis with cross-linked aggregates of Bacillus circulans β-galactosidase
    Process Biochemistry, 2020
    Co-Authors: Cecilia Guerrero, Carlos Vera, Sebastián Suárez, Carla Aburto, Claudia Ubilla, Nicolás Ramírez, Andrés Illanes
    Abstract:

    Abstract Synthesis of lactulose with crosslinked aggregates of Bacillus circulans β-galactosidase (CLAGs) has been compared in Batch and repeated-Batch Operation for the first time. The effect of the type of the precipitating agent and its concentration, the crosslinker concentration and the time of crosslinking were evaluated for their effect on the parameters: immobilization yield, specific activity and thermal stability of the biocatalysts. The type and concentration of the precipitating agent were the variables that produced a significant variation in the immobilization parameters of the biocatalyst. CLAGs were obtained with a specific activity of 7790 IUH⋅g−1 at an immobilization yield of 46.2 % using 50 % v/v of propanol as precipitating agent, 5.5 gglutarldehyde gprotein−1 for crosslinking and 1 h of crosslinking time. This biocatalyst was more stable than the free enzyme with a stabilization factor of 11.3 h at 50 °C. Highest yield of lactulose synthesis with CLAGs was 0.42 g g−1 for a fructose/lactose molar ratio of 8. Repeated-Batch Operation allowed a significant increase in lactulose production per unit mass of biocatalyst and in cumulative productivity with respect to Batch Operation, yielding an efficiency of biocatalyst use of 2.43 kglactulose gbiocatalyst protein−1.

  • Fed-Batch Operation for the synthesis of lactulose with β-galactosidase of Aspergillus oryzae
    Bioresource Technology, 2017
    Co-Authors: Cecilia Guerrero, Carlos Vera, Andrés Illanes
    Abstract:

    Abstract Fed-Batch synthesis of lactulose from lactose and fructose with Aspergillus oryzae β-galactosidase was evaluated, obtaining a concentration of 40.4 g·L−1, which is 20% higher than obtained in Batch, while the concentration of transgalactosylated oligosaccharides (TOS) was reduced by 98%. Therefore, selectivity of lactulose synthesis can be significantly higher by operating in fed-Batch mode. The enzyme-limiting substrate mass ratio (E/S) is a critical variable in fed-Batch Operation. Higher values favor lactose hydrolysis over transgalactosylation, being 400 IU/g the limit for proper lactulose synthesis in fed-Batch Operation. Selectivity of lactulose synthesis increased with E/S being quite high at 800 IUH·g−1 or higher. However, this increase was obtained at the expense of lactulose yield. Lactulose synthesis in fed-Batch Operation was a better option than conventional Batch synthesis, since higher product concentration and selectivity of lactulose over TOS synthesis were obtained.

  • Fed-Batch Operation for the synthesis of lactulose with β-galactosidase of Aspergillus oryzae
    Bioresource Technology, 2017
    Co-Authors: Cecilia Guerrero, Carlos Vera, Andrés Illanes
    Abstract:

    Abstract Fed-Batch synthesis of lactulose from lactose and fructose with Aspergillus oryzae β-galactosidase was evaluated, obtaining a concentration of 40.4 g·L−1, which is 20% higher than obtained in Batch, while the concentration of transgalactosylated oligosaccharides (TOS) was reduced by 98%. Therefore, selectivity of lactulose synthesis can be significantly higher by operating in fed-Batch mode. The enzyme-limiting substrate mass ratio (E/S) is a critical variable in fed-Batch Operation. Higher values favor lactose hydrolysis over transgalactosylation, being 400 IU/g the limit for proper lactulose synthesis in fed-Batch Operation. Selectivity of lactulose synthesis increased with E/S being quite high at 800 IUH·g−1 or higher. However, this increase was obtained at the expense of lactulose yield. Lactulose synthesis in fed-Batch Operation was a better option than conventional Batch synthesis, since higher product concentration and selectivity of lactulose over TOS synthesis were obtained.

  • Repeated-Batch Operation for the synthesis of lactulose with β-galactosidase immobilized by aggregation and crosslinking
    Bioresource technology, 2015
    Co-Authors: Cecilia Guerrero, Carlos Vera, Erick Araya, Raúl Conejeros, Andrés Illanes
    Abstract:

    Abstract Synthesis of lactulose under repeated-Batch Operation was done with cross-linked aggregates of Aspergillus oryzae β-galactosidase (CLAGs). The effect of the crosslinking agent to enzyme mass ratio and cross-linking time were first evaluated. Best results were obtained at 5.5 g de glutaraldehyde/g enzyme at 5 h of cross-linking, obtaining a specific activity of 15,000 IU g −1 , with 30% immobilization yield. CLAG was more stable than the free enzyme under non-reactive conditions with a half-life of 123 h at 50 °C and when operated in repeated-Batch mode, yield and productivity was 3.8 and 4.3 times higher. Maximum number of Batches was determined considering biocatalyst replacement at 50% residual activity. 98 and 27 Batches could be performed under such criterion at fructose/lactose molar ratio of 4 and 20 respectively, reflecting that enzyme stability is strongly affected by the sugars distribution in the reaction medium.

  • Immobilization of Bacillus circulans β-galactosidase and its application in the synthesis of galacto-oligosaccharides under repeated-Batch Operation
    Biochemical Engineering Journal, 2013
    Co-Authors: Paulina Urrutia, Cesar Mateo, J.m. Guisán, Lorena Wilson, Andrés Illanes
    Abstract:

    Abstract A highly active and stable derivate of immobilized Bacillus circulans β-galactosidase was prepared for the synthesis of galacto-oligosaccharides (GOS) under repeated-Batch Operation. B. circulans β-galactosidase was immobilized on monofunctional glyoxyl agarose and three heterofunctional supports: amino-, carboxy-, and chelate-glyoxyl agarose. Glyoxyl agarose was the support with highest immobilization yield and stability being selected for the optimization of immobilization conditions and application in GOS synthesis. A central composite rotatable design was conducted to optimize contacted protein and immobilization time, using maximum catalytic potential as the objective function. Optimal conditions of immobilization were 28.9 mg/g and 36.4 h of contact, resulting in a biocatalyst with 595 IU/g and a half-life 89-fold higher than soluble enzyme. Immobilization process did not alter the synthetic capacity of β-galactosidase, obtaining the same GOS yield and product profile than the free enzyme. GOS yield and productivity remained unchanged along 10 repeated Batches, with values of 39% (w/w) and 5.7 g GOS/g of biocatalyst·Batch. Total product obtained after 10 Batches of reaction was 56.5 g GOS/g of biocatalyst (1956 g GOS/g protein). Cumulative productivity in terms of mass of contacted protein was higher for the immobilized enzyme than for its soluble counterpart from the second Batch of synthesis onwards.